Thin film transistor substrate and display using the same

ABSTRACT

The present disclosure relates to a thin film transistor substrate having two different types of thin film transistors on the same substrate, and a display using the same. A display includes a first thin film transistor including a poly crystalline semiconductor layer, a first gate electrode on the poly crystalline semiconductor layer, a first source electrode, and a first drain electrode; a second thin film transistor including a second gate electrode, an oxide semiconductor layer on the second gate electrode, a second source electrode, and a second drain electrode; and an intermediate insulating layer including a nitride layer and an oxide layer on the nitride layer, the intermediate insulating layer disposed on the first gate electrode and the second gate electrode and under the oxide semiconductor layer.

This application claims the benefit of Korean Patent App. No.10-2014-0021500, filed in Korea on Feb. 24, 2014; and No.10-2015-0025178, filed on Feb. 23, 2015, the entire disclosure of eachof which is hereby incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a thin film transistor substratehaving two different types of thin film transistors on the samesubstrate, and a display using the same.

2. Discussion of the Related Art

Nowadays, as the information society is developed, the requirements ofdisplays for representing information are increasing. Accordingly,various flat panel displays (or ‘FPD’) are developed for overcoming manydrawbacks of the cathode ray tube (or ‘CRT’) such as heavy weight andbulk volume. Flat panel display devices include a liquid crystal displaydevice (or ‘LCD’), a plasma display panel (or ‘PDP’), a organic lightemitting display device (or ‘OLED’) and a electrophoresis display device(or ‘ED’).

The display panel of a flat panel display may include a thin filmtransistor substrate having a thin film transistor allocated in eachpixel region arrayed in a matrix manner. For example, the liquid crystaldisplay device (or ‘LCD’) represents video data by controlling the lighttransitivity of the liquid crystal layer using electric fields. Theorganic light emitting diode display represents video data by generatingproperly controlled light at each pixel disposed in a matrix mannerusing an organic light emitting diode formed in each pixel.

As a self-emitting display device, the organic light emitting diodedisplay device has merits including very fast response speed, highbrightness, and large viewing angle. The organic light emitting diodedisplay (or OLED) using the organic light emitting diode having goodenergy efficiency can be categorized in the passive matrix type organiclight emitting diode display (or PMOLED) and the active matrix typeorganic light emitting diode display (or AMOLED).

As personal appliances have been more adopted, portable and/or wearabledevices have been actively developed. To apply the display device for aportable and/or wearable device, the device should have low powerconsumption. However, using already developed technologies, a limitationhas been getting a display with low power consumption.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a thin film transistorsubstrate and display using the same that substantially obviate one ormore of the problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide a thin film transistorsubstrate for a flat panel display having at least two transistorshaving different characteristics from each other on the same substrate.

Another object of the present invention is to provide a thin filmtransistor substrate for a flat panel display having two different typesof transistors manufactured with an efficient manufacturing process andreduced number of mask processes.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a displaycomprises a first thin film transistor including a poly crystallinesemiconductor layer, a first gate electrode on the poly crystallinesemiconductor layer, a first source electrode, and a first drainelectrode; a second thin film transistor including a second gateelectrode, an oxide semiconductor layer on the second gate electrode, asecond source electrode, and a second drain electrode; and anintermediate insulating layer including a nitride layer and an oxidelayer on the nitride layer, the intermediate insulating layer disposedon the first gate electrode and the second gate electrode and under theoxide semiconductor layer.

In another aspect, a display comprises a first semiconductor layerincluding a poly crystalline semiconductor material; a gate insulatinglayer covering the first semiconductor layer; a first gate electrodedisposed on the gate insulating layer and overlapping the firstsemiconductor layer; a second gate electrode disposed on the gateinsulating layer; an intermediate insulating layer including a nitridelayer and an oxide layer on the nitride layer, and covering the firstgate electrode and the second gate electrode; a second semiconductorlayer disposed on the intermediate insulating layer, including an oxidesemiconductor material and overlapping the second gate electrode; afirst source electrode and a first drain electrode disposed on theintermediate insulating layer; and a second source electrode, and asecond drain electrode disposed on the second semiconductor layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttype thin film transistors are formed according to a first embodiment ofthe present disclosure.

FIG. 2 is a flow chart illustrating a method for manufacturing the thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed according to the firstembodiment of the present disclosure.

FIG. 3 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttypes of thin film transistors are formed, according to a secondembodiment of the present disclosure.

FIG. 4 is a flow chart illustrating a method for manufacturing the thinfilm transistor substrate for a flat panel display in which twodifferent types of thin film transistors are formed according to thesecond embodiment of the present disclosure.

FIG. 5 is a block diagram illustrating a structure of a displayaccording to a first application example of the present disclosure.

FIG. 6 is a plane view illustrating a thin film transistor substratehaving an oxide semiconductor layer included in a fringe field typeliquid crystal display according to a second application example of thepresent disclosure.

FIG. 7 is a cross-sectional view illustrating the structure of the thinfilm transistor substrate of FIG. 6 by cutting along the line I-I′according to the second application example of the present disclosure.

FIG. 8 is a plane view illustrating the structure of one pixel for theactive matrix type organic light emitting diode display having activeswitching elements, such as thin film transistors, according to a thirdapplication embodiment of the present disclosure.

FIG. 9 is a cross sectional view illustrating the structure of theorganic light emitting diode display along to the cutting line II-IF inFIG. 8 according to a third application embodiment of the presentdisclosure.

FIG. 10 is an enlarged plane view illustrating a structure of an organiclight emitting diode display according to a fourth applicationembodiment of the present disclosure.

FIG. 11 is a cross sectional view illustrating a structure of theorganic light emitting diode display along the cutting line III-III′ inFIG. 10 according to a fourth application embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Like reference numerals designate like elements throughout thedetailed description. However, the present disclosure is not restrictedby these embodiments but can be applied to various changes ormodifications without changing the technical spirit. In the followingembodiments, the names of the elements are selected for ease ofexplanation and may be different from actual names. Hereinafter, themeaning for the term of “on” includes “directly on” and “indirectly on”in all scopes of the specification. Similarly, the meaning for the termof “over” includes “directly over” and “indirectly over” in all scopesof the specification. Further, the meaning for the term of “under”includes “directly under” and “indirectly under” in all scopes of thespecification.

The thin film transistor substrate for a flat panel display according tothe present disclosure comprises a first thin film transistor disposedin a first area and a second thin film transistor disposed in a secondarea, on the same substrate. The substrate may include a display areaand a non-display area. In the display area, a plurality of pixel areais arrayed in a matrix manner. In one pixel area, the display elementsare disposed. In the non-display area surrounding the display area, thedriver elements for driving the display elements in the pixel area aredisposed.

Here, the first area may be the non-display area, and the second areamay be some portions or all portions of the display area. In this case,the first thin film transistor and the second thin film transistor aredisposed as they may be apart from each other. Otherwise, the first areaand the second area may be included in the display area. Especially, forthe case that a plurality of thin film transistor are disposed in onepixel area, the first thin film transistor and the second thin filmtransistor may be closely disposed.

As the poly crystalline semiconductor material has the characteristicsof high mobility (over 100 cm²/Vs) and of low energy consumption power,and it has high reliability, it is proper to apply to the driver IC,such as the gate driver and/or the multiplexer (or ‘MUX’) for drivingthe display elements. In addition, it can be applied to the driving thinfilm transistor disposed in the pixel area of the organic light emittingdiode display. As the oxide semiconductor material has low off-current,it is proper to apply to the channel layer of the switching thin filmtransistor in the pixel area, in which the ON time period is very shortbut the OFF time period is long. Further, as the off-current is low, theholding time of the pixel voltage may be long, so that it is preferableto apply the display with low frequency drive and/or low powerconsumption. By disposing these two different type thin filmtransistors, the present disclosure suggests a thin film transistorsubstrate having an optimized function and characteristic for theportable and/or wearable displays.

When the semiconductor layer is formed using the poly crystallinesemiconductor material, the doping process and high temperaturetreatment process are used. On the contrary, when the semiconductorlayer is formed using the oxide semiconductor material, it is performedunder a relatively lower temperature process. Therefore, it ispreferable that the poly crystalline semiconductor layer, performedunder a more severe heat condition, is first formed, and after that, theoxide semiconductor layer is formed. To do so, in the presentdisclosure, the first thin film transistor having the poly crystallinesemiconductor material may have a top gate structure, and the secondthin film transistor having the oxide semiconductor material would havea bottom gate structure.

Further, in view of manufacturing process, when the poly crystallinesemiconductor material has a lot of vacancy, the characteristics may beseverely degraded. Therefore, a hydrogenation process may be performedin which the vacancies are filled with hydrogen particles. On the otherhand, for the oxide semiconductor material, the vacancies may act as thecarriers, so it may be desired that the thermal treatment be performedwith a small amount of vacancies in the oxide semiconductor material.These processes, the hydrogenation process and the thermal treatment,can be performed by a post-thermal process under a 350˜380° C.temperature condition.

For the hydrogenation process, a nitride layer having a lot of hydrogenparticles may be provided over the poly crystalline semiconductormaterial. As the materials used for depositing the nitride layer has alarge amount of hydrogen, a lot of hydrogen particles may be includedinto the deposited nitride layer. By the thermal process, the hydrogenparticles can be diffused into the poly crystalline semiconductormaterial. As the result, the poly crystalline semiconductor layer can bestabilized. During the thermal process, too much of the hydrogenparticles should not be diffused into the oxide semiconductor material.Therefore, an oxide layer should be disposed between the nitride layerand the oxide semiconductor material. As a result, the oxidesemiconductor layer can be stabilized but may be affected too much bythe hydrogen particles.

Hereinafter, for convenience, the first thin film transistor is for thedriver IC disposed in the non-display area and the second thin filmtransistor is for the display element disposed in the pixel area of thedisplay area. However, embodiments are not restricted to this case. Forexample, in a organic light emitting diode display, the first thin filmtransistor and the second thin film transistor may be disposed at onepixel area in the display area. Especially, the first thin filmtransistor having the poly crystalline semiconductor material may beapplied for the driving thin film transistor, and the second thin filmtransistor having the oxide semiconductor material may be applied forthe switching thin film transistor.

First Embodiment

FIG. 1 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttype thin film transistors are formed according to a first embodiment ofthe present disclosure. Here, the cross sectional views more clearly andconveniently show the main features of the present disclosure.

With reference to FIG. 1, the thin film transistor substrate for a flatpanel display according to the first embodiment comprises a first thinfilm transistor T1 and a second thin film transistor T2 which aredisposed on the same substrate SUB. The first and second thin filmtransistors T1 and T2 may be far apart from each other, or they may bedisposed within a relatively close distance. Otherwise, these two thinfilm transistors are disposed as being overlapping each other.

On the whole surface of the substrate SUB, a buffer layer BUF isdeposited. In some cases, the buffer layer BUF may not be included. Or,the buffer layer BUF may be a plurality of layers. Here, forconvenience, a single layer arrangement will be explained. Further, alight shield layer may be included at some areas between the substrateSUB and the buffer layer BUF. The light shield layer may be furtherdisposed to prevent the light from inducing into the semiconductor layerof the thin film transistor disposed thereon.

On the buffer layer BUF, a first semiconductor layer A1 is disposed. Thefirst semiconductor layer A1 includes a channel area of the first thinfilm transistor T1. The channel area is defined as the overlapped areabetween the first gate electrode G1 and the first channel layer A1. Asthe first gate electrode G1 is overlapped with the middle portions ofthe first semiconductor layer A1, the middle portion of the firstsemiconductor layer A1 is the channel area. The two areas expanded toboth sides of the channel area where the impurities are doped aredefined as the source area SA and the drain area DA, respectively.

For the case that the first thin film transistor T1 is for the driverIC, it is preferable that the semiconductor layer has a characteristicfor high speed performance with a lower power consumption. For example,P-MOS type or N-MOS type thin film transistor may be used, or C-MOS typemay be applied for the first thin film transistor T1. The P-MOS, N-MOSand/or C-MOS type thin film transistor preferably has a poly crystallinesemiconductor material, such as poly-crystalline silicon (p-Si).Further, the first thin film transistor T1 preferably has a top gatestructure.

On the whole surface of the substrate SUB having the first semiconductorlayer A1, a gate insulating layer GI is deposited. The gate insulatinglayer GI may be made of the silicon nitride (SiNx) material or thesilicon oxide (SiOx) material. It may be preferable that the gateinsulating layer GI has the thickness of 1,000 Å˜1,500 Å for ensuringthe stability and characteristics of the elements. In the case that thegate insulating layer GI may be made of silicon nitride (SiNx), in theview point of manufacturing process, the gate insulating layer GIincludes a lot of hydrogen particles. As these hydrogen particles wouldbe diffused out from the gate insulating layer GI, it is preferable thatthe gate insulating layer GI is made of silicon oxide material.

The diffusion of the hydrogen particles may cause positive effects onthe first semiconductor layer A1 including poly crystallinesemiconductor material. However, it may cause negative effects on thesecond thin film transistor T2 having different material from the firstthin film transistor T1. Therefore, when at least two thin filmtransistors having different characteristics from each other are formedon the same substrate SUB, it is preferable that the gate insulatinglayer GI would be made of silicon oxide (SiOx), which is less likely toaffect the semiconductor material. In some cases, unlike in the firstembodiment, the gate insulating layer GI may be deposited as having thethickness of 2,000 Å˜4,000 Å. In those cases, when the gate insulatinglayer GI is made of the nitride silicon (SiNx), much more of thehydrogen particles may be diffused. Considering these cases, it ispreferable that the gate insulating layer GI would be the oxide layer,such as silicon oxide (SiOx).

On the gate insulating layer GI, a first gate electrode G1 and a secondgate electrode G2 are disposed. The first gate electrode G1 is disposedover the middle portion of the first semiconductor layer A1. The secondgate electrode G2 is located where the second thin film transistor T2 isdisposed. The first and the second gate electrodes G1 and G2 are formedon the same layer, with the same material, and by using the same maskprocess. Therefore, the manufacturing process can be simplified.

An intermediate insulating layer ILD is deposited covering the first andthe second gate electrodes G1 and G2. The intermediate insulating layerILD has a multiple layer structure, in which a nitride layer SINincluding a silicon nitride (SiNx) and an oxide layer SIO including asilicon oxide (SiOx) are alternatively stacked. Here, for convenience ofexplanation, the intermediate insulating layer ILD, as described,includes two layers in which the oxide layer SIO is stacked on thenitride layer SIN.

The nitride layer SIN is deposited for performing the hydrogenationprocess to the first semiconductor layer A1 having the poly crystallinesilicon by diffusing the hydrogen particles into the poly crystallinesilicon. On the contrary, the oxide layer SIO is for preventing thehydrogen particles of the nitride layer SIN from being diffused too muchinto the semiconductor material of the second thin film transistor T2.

For example, the hydrogen going out from the nitride layer SIN maydiffuse into the first semiconductor layer A1 under the gate insulatinglayer GI. Therefore, the nitride layer SIN is preferably deposited asclose to the gate insulating layer GI as possible. On the contrary, thehydrogen going out from the nitride layer SIN would not diffuse too muchinto the semiconductor material of the second thin film transistor T2over the gate insulating layer GI. Therefore, on the nitride layer SIN,the oxide layer SIO should be deposited. Considering the manufacturingprocess, it is preferable that the intermediate insulating layer ILD hasthe thickness of 2,000 Å˜6,000 Å. Therefore, each thickness of thenitride layer SIN and the oxide layer SIO preferably have a thickness of1,000 Å˜3,000 Å, respectively. Further, in order that much more amountof the hydrogen particles from the nitride layer SIN into the firstsemiconductor layer A1, but the hydrogen particles may not affect thesecond semiconductor layer A2, it is preferable that the oxide layer SIOis thicker than the gate insulating layer GI. In addition, as the oxidelayer SIO is for controlling the hydrogen diffusion amount, it ispreferable that the oxide layer SIO is thicker than the nitride layerSIN.

Especially, on the oxide layer SIO of the intermediate insulating layerILD, a second semiconductor layer A2 overlapping with the second gateelectrode G2 is disposed. The second semiconductor layer A2 includes thechannel area of the second thin film transistor T2. For the case thatthe second thin film transistor T2 is applied for the display element,it is preferable that the second semiconductor layer A2 hascharacteristics proper to perform the switching element. For example, itis preferable that the second semiconductor layer A2 includes an oxidesemiconductor material, such as indium gallium zinc oxide (or ‘IGZO’),indium gallium oxide (or ‘IGO’), or indium zinc oxide (or ‘IZO’). Theoxide semiconductor material has a merit for driving the device withrelatively low frequency. Due to these characteristics, the pixels mayhave a long period for holding the pixel voltage, and consequentially,it may be desirable to apply the display with a low frequency driveand/or low power consumption. For the thin film transistor having theoxide semiconductor material, considering the structure in which twodifferent type thin film transistors are formed on the same substrate,it is preferable that the oxide semiconductor thin film transistor has abottom gate structure for ensuring the stability of the elements.

On the second semiconductor layer A2 and the intermediate insulatinglayer ILD, the source-drain electrodes are disposed. The first sourceelectrode S1 and the first drain electrode D1 are disposed facing eachother with a predetermined distance across the first gate electrode G1.The first source electrode S1 is connected to one side of the firstsemiconductor layer A1, a source area SA through a source contact holeSH. The source contact hole SH exposes the one side of the firstsemiconductor layer A1, the source area SA, by penetrating theintermediate insulating layer ILD and the gate insulating layer GI. Thefirst drain electrode D1 is connected to the other side of the firstsemiconductor layer A1, a drain area DA, through a drain contact holeDH. The drain contact hole DH exposes the other side of the firstsemiconductor layer A1, the drain area DA, by penetrating theintermediate insulating layer ILD and the gate insulating layer GI.

The second source electrode S2 and the second drain electrode D2 aredisposed facing each other with a predetermined distance across thesecond gate electrode G2, and contacting the upper surfaces of the oneside and the other side of the second semiconductor layer A2. The secondsource electrode S2 directly contacts the upper surface of theintermediate insulating layer ILD and the one upper surface of thesecond semiconductor layer A2. The second drain electrode D2 directlycontacts the upper surface of the intermediate insulating layer ILD andthe other upper surface of the second semiconductor layer A2.

On the whole surface of the substrate SUB having the first thin filmtransistor T1 and the second thin film transistor T2, a passivationlayer PAS is deposited. Further, by patterning the passivation layerPAS, contact holes for exposing the first drain electrode D1 and/or thesecond drain electrode D2 may be included. In addition, on thepassivation layer PAS, a pixel electrode (e.g., an anode electrode forthe organic light emitting diode display) may be included as connectingto the first drain electrode D1 and/or second drain electrode D2. Here,for convenience, the structure of the thin film transistor showing themain features of the present disclosure will be explained.

As mentioned above, the thin film transistor substrate for the flatpanel display according to the first embodiment of the presentdisclosure suggests the structure in which the first thin filmtransistor T1 has a poly crystalline semiconductor material and thesecond thin film transistor T2 has an oxide semiconductor material, onthe same one substrate SUB. Especially, the first gate electrode G1 ofthe first thin film transistor T1 and the second gate electrode G2 ofthe second thin film transistor T2 are formed on the same layer with thesame metal material.

The first semiconductor layer A1 of the first thin film transistor T1having the poly crystalline semiconductor material is disposed under thefirst gate electrode G1, but the second semiconductor layer A2 of thesecond thin film transistor T2 having the oxide semiconductor materialis disposed over the second gate electrode G2. The first semiconductorlayer A1 which may be manufactured under a relatively higher temperaturecondition is formed first. After that, the second semiconductor layerA2, which may be manufactured under the relatively lower temperaturecondition, is formed. As a result, the oxide semiconductor material isnot exposed by the high temperature condition, during the wholemanufacturing processes. As the first semiconductor layer A1 is formedbefore forming the first gate electrode G1, the first thin filmtransistor T1 has a top-gate structure. As the second semiconductorlayer A1 is formed after forming the second gate electrode G2, thesecond thin film transistor T2 a the bottom-gate structure.

Further, in the thermal treatment process for the second semiconductorlayer A2 including the oxide semiconductor material, the hydrogenationprocess for the first semiconductor layer A1 including the polycrystalline semiconductor material can be performed, at the same time.To do so, it is preferable that the intermediate insulating layer ILDincludes two stacked layers as disposing an oxide layer SIO over anitride layer SIN. In the view of manufacturing process, a hydrogenationmay be used for diffusing the hydrogen particles into the firstsemiconductor layer A1. Further, it is advantageous for performing athermal treatment for stabilizing the second semiconductor layer A2including the oxide semiconductor material. The hydrogenation processmay be performed after depositing the nitride layer SIN on the firstsemiconductor layer A1, and the thermal treatment may be performed afterforming the second semiconductor layer A2. According to the firstembodiment of the present disclosure, as the oxide layer SIO isdeposited between the nitride layer SIN and the second semiconductorlayer A2, the hydrogen particles can be prevented from diffusing toomuch into the second semiconductor layer A2 including the oxidesemiconductor material. Therefore, in this first embodiment of thepresent disclosure, during the thermal treatment for the oxidesemiconductor material, the hydrogenation process may be performed atthe same time.

FIG. 2 is a flow chart illustrating a method for manufacturing a thinfilm transistor substrate having two different types of thin filmtransistors according to the first embodiment of the present disclosure.

In step S100, on a substrate SUB, a buffer layer BUF is deposited. Eventhough it is not shown in figures, before depositing the buffer layerBUF, a light shield layer may be formed at a desired area.

In step S110, on the buffer layer BUF, an amorphous silicon (a-Si)material is deposited. Performing the crystallization process, theamorphous silicon layer is converted into the poly crystalline silicon(poly-Si). Using a first mask process, the poly crystalline siliconlayer is patterned to form a first semiconductor layer A1.

In step S120, by depositing an insulating material, such as siliconoxide, on the whole surface of the substrate SUB having the firstsemiconductor layer A1, a gate insulating layer GI is formed. The gateinsulating layer GI preferably includes the silicon oxide. Here, thegate insulating layer GI preferably has a thickness of 1,000 Å or moreand 1,500 Å or less.

In step S200, on the gate insulating layer GI, a gate metal material isdeposited. Using a second mask process, the gate metal layer ispatterned to form the gate electrodes. Especially, a first gateelectrode G1 for the first thin film transistor T1 and a second gateelectrode G2 for the second thin film transistor T2 are formed at thesame time. The first gate electrode GI is disposed as overlapping withthe middle portion of the first semiconductor layer A1. The second gateelectrode G2 is disposed where the second thin film transistor T2 isformed.

In step S210, using the first gate electrode G1 as a mask, impuritymaterials are doped into some portions of the first semiconductor layerA1 so that doping areas including a source area SA and a drain area DAmay be defined. The detailed manufacturing process for the doping areasmay be little bit different according to the types of thin filmtransistor (e.g., P-MOS type, N-MOS type and/or C-MOS type). For examplefor the N-MOS type, a high density doping area may be formed first, andthen a low density doping area may be formed. Using the photo-resistpattern for the first gate electrode G1 which has a wider size than thefirst gate electrode G1, the high density doping area can be defined.Removing the photo-resist pattern and using the first gate electrode G1as a mask, the low density doping area (or, ‘LDD’) can be definedbetween the high density doping area and the first gate electrode G1.The impurity doping areas are not shown in the figures, for convenience.

In step S220, on the whole surface of the substrate SUB having the firstgate electrode G1 and the second gate electrode G2, an intermediateinsulating layer ILD is deposited. Especially, a nitride layer SIN isfirstly deposited and then an oxide layer SIO is sequentially depositedthereon. The nitride layer SIN includes a lot of hydrogen particlesduring the depositing process. Considering the manufacturing process,the total thickness of the intermediate insulating layer ILD may have athickness of 2,000 Å˜6,000 Å. Here, for the nitride layer SIN of whichpurpose is the diffusion of the hydrogen particles, considering thehydrogenation efficiency, it preferably has a thickness of 1,000 Å˜3,000Å. As the oxide layer SIO is for preventing the hydrogen particle fromdiffusing too much into the semiconductor layer disposed over the oxidelayer SIO, it preferably has the thickness of 1,000 Å˜3,000 Å.Considering the hydrogen diffusion efficiency and the elementproperties, the thicknesses of the oxide layer SIO and the nitride layerSIN may preferably be selected and/or decided. For example, in order toprevent the hydrogen particles from diffusing out too much, the nitridelayer SIN is preferably thinner than the oxide layer SIO.

In step S300, on the intermediate insulating layer ILD, especially onthe oxide layer SIO, an oxide semiconductor material is deposited.Further, the oxide semiconductor material is preferably depositeddirectly on the oxide layer SIO in order that the oxide semiconductormaterial does not directly contact the nitride layer SIN including thehydrogen particles a lot. The oxide semiconductor material includes atleast one of Indium Gallium Zinc Oxide (or ‘IGZO’), Indium Gallium Oxide(or ‘IGO’), and Indium Zinc Oxide (or ‘IZO’). Using a third maskprocess, the oxide semiconductor material is patterned to form a secondsemiconductor layer A2. The second semiconductor layer A2 is disposed asoverlapping with the second gate electrode G2.

In step S310, performing a post-thermal process to the substrate SUBhaving the second semiconductor layer A2, the hydrogenation for thefirst semiconductor layer A1 including the poly crystalline silicon andthe thermal treatment for the second semiconductor layer A2 includingthe oxide semiconductor material are performed at the same time. Thepost-thermal process may be performed under a 350˜380° C. temperaturecondition. At this time, a large amount of the hydrogen particlesincluded in the nitride layer SIN would be diffused into the firstsemiconductor layer A1. However, the amount of the hydrogen particlesdiffused into the second semiconductor layer A2 may be restricted and/orcontrolled by the oxide layer SIO. In some cases, the hydrogenationprocess for the first semiconductor layer A1 is performed separatelyfrom the thermal treatment for the second semiconductor layer A2. Inthese cases, the hydrogenation process is first performed after stepS220 for depositing the intermediate insulating layer ILD, and then thethermal treatment for the second semiconductor layer A2 is performed bythis post-thermal process.

In step S400, using a fourth mask process, the intermediate insulatinglayer ILD and the gate insulating layer GI are patterned to form asource contact hole SH exposing the one portion of the firstsemiconductor layer A1 and a drain contact hole DH exposing the otherportion of the first semiconductor layer A1. These contact holes SH andDH are for later connecting the source-drain electrode to the firstsemiconductor layer A1.

Here, steps S300, S310, and S400 may be changed in sequential order, inaccordance with the manufacturing conditions. For example, step S400 forforming the contact holes may be performed first, step S300 for formingthe second semiconductor layer A2 may be performed second, then stepS310 for performing the post-thermal treatment may be performed finally.Otherwise, step S300 for forming the second semiconductor layer A2 maybe performed first, step S400 for forming the contact holes may beperformed second, then step S310 for performing the post-thermaltreatment may be performed finally.

In step S500, a source-drain metal material is deposited on theintermediate layer ILD having the source contact hole SH, the draincontact hole DH, and the second semiconductor layer A2. Using a fifthmask process, the source-drain metal material is patterned to form afirst source electrode S1, a first drain electrode D1, a second sourceelectrode S2 and a second drain electrode D2. The first source electrodeS1 contacts one area of the first semiconductor layer A1, the sourcearea SA, through the source contact hole SH. The first drain electrodeD1 contacts another area of the first semiconductor layer A1, the drainarea DA, through the drain contact hole DH. The second source electrodeS2 contacts the upper surface of one side of the second semiconductorlayer A2. The second drain electrode D2 contacts the upper surface ofthe other side of the second semiconductor layer A2.

In step S600, on the whole surface of the substrate SUB having thesource-drain electrodes, a passivation layer PAS is deposited. Eventhough not shown in the figures, the passivation layer PAS may bepatterned to form contact holes for exposing some portions of the firstand/or second drain electrodes D1 and/or D2.

Second Embodiment

FIG. 3 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttypes of thin film transistors are formed according to a secondembodiment of the present disclosure.

The thin film transistor substrate according to the second embodiment isbasically very similar to that of the first embodiment. The maindifference is on the intermediate layer ILD includes three layers.Especially, the intermediate layer ILD includes a lower oxide layerSIO1, a nitride layer SIN and an upper oxide layer SIO2, stackedsequentially.

The intermediate layer ILD also acts as a gate insulating layer for thesecond thin film transistor T2. Therefore, when the intermediate layerILD is too thick, the gate voltage many not be properly applied to thesecond semiconductor layer A2. Therefore, the whole thickness of theintermediate layer ILD preferably has a thickness of 2,000 Å˜6,000 Å.

By the post-thermal process, the hydrogen particles in the nitride layerSIN would be diffused into the first semiconductor layer A1. Inconsideration of the diffusion efficiency, it is preferable that thelower oxide layer SIO1 has a thickness of 500 Å˜1,500 Å, and the nitridelayer SIN has a thickness of 1,000 Å˜2,000 Å. As the upper oxide layerSIO2 is for restricting the diffusion of hydrogen into the secondsemiconductor layer A2, it is preferable that the upper oxide layer SIO2has the thickness of 1,000 Å˜3,000 Å. Especially, as the upper oxidelayer SIO2 is for controlling the hydrogen diffusion amount, it ispreferable that the upper oxide layer SIO2 is thicker than the nitridelayer SIN.

As other elements are similar with those of the first embodiment, adetailed explanation is omitted. Hereinafter, the method formanufacturing the thin film transistor substrate for flat panel displayaccording to the second embodiment of the present disclosure will beexplained. Here, the duplicated explanations having no extra meaning arenot mentioned.

FIG. 4 is a flow chart illustrating a method for manufacturing a thinfilm transistor substrate for a flat panel display in which twodifferent types of thin film transistors are formed according to thesecond embodiment of the present disclosure.

In step S100, on a substrate SUB, a buffer layer BUF is deposited. Instep S110, on the buffer layer BUF, an amorphous silicon (a-Si) materialis deposited. Performing the crystallization process, the amorphoussilicon layer is converted into the poly crystalline silicon (poly-Si).Using a first mask process, the poly crystalline silicon layer ispatterned to form a first semiconductor layer A1.

In step S120, by depositing an insulating material, such as siliconoxide, on the whole surface of the substrate SUB having the firstsemiconductor layer A1, a gate insulating layer GI is formed. The gateinsulating layer GI is preferably made of silicon oxide with a thicknessof 1,000 Å˜1,500 Å.

In step S200, on the gate insulating layer GI, a gate metal material isdeposited. Using a second mask process, the gate metal layer ispatterned to form the gate electrodes. Especially, a first gateelectrode G1 for the first thin film transistor T1 and a second gateelectrode G2 for the second thin film transistor T2 are formed at thesame time. The first gate electrode G1 is disposed as overlapping withthe middle portion of the first semiconductor layer A1. The second gateelectrode G2 is disposed where the second thin film transistor T2 isformed.

In step S210, using the first gate electrode G1 as a mask, impuritymaterials are doped into some portions of the first semiconductor layerA1 so that doping areas including a source area SA and a drain area DAmay be defined.

In step S220, on the whole surface of the substrate SUB having the firstgate electrode G1 and the second gate electrode G2, an intermediateinsulating layer ILD is deposited. Especially, the intermediate layerILD has a three-layered structure in which a lower oxide layer SIO1, anitride layer SIN and an upper oxide layer SIO2 are sequentiallydeposited. As the lower oxide layer SIO1 is for compensating the damagedsurface condition of the gate insulating layer GI during the patterningprocess for the gate electrodes G1 and G2, it preferably has a thicknessof 500 Å˜1,000 Å. The nitride layer SIN has a thickness of 1,000 Å˜2,000Å, and the upper oxide layer SIO2 has a thickness of 1,000 Å˜3,000 Å.Considering the hydrogen diffusion efficiency and the elementproperties, the thicknesses of the oxide layer SIO and the nitride layerSIN may preferably be selected and/or decided. For example, to preventthe hydrogen particles from diffusing out too much, the nitride layerSIN is preferably thinner than the oxide layer SIO.

In step S300, on the intermediate insulating layer ILD, an oxidesemiconductor material is deposited. Especially, the oxide semiconductormaterial is preferably deposited directly on the oxide layer SIO inorder not to contact the nitride layer SIN having a lot of hydrogen.Using a third mask process, the oxide semiconductor material ispatterned to form a second semiconductor layer A2. The secondsemiconductor layer A2 is disposed as overlapping with the second gateelectrode G2.

In step S310, performing a post-thermal process on the substrate SUBhaving the second semiconductor layer A2, the hydrogenation for thefirst semiconductor layer A1 including the poly crystalline silicon andthe thermal treatment for the second semiconductor layer A2 includingthe oxide semiconductor material are performed at a same time. Thepost-thermal process may be performed under a 350˜380° C. temperaturecondition. At this time, a large amount of the hydrogen particlesincluded into the nitride layer SIN are diffused into the firstsemiconductor layer A1. However, the amount of the hydrogen particlesdiffused into the second semiconductor layer A2 may be restricted and/orcontrolled by the oxide layer SIO. In some cases, the hydrogenationprocess for the first semiconductor layer A1 may be performed separatelyfrom the thermal treatment for the second semiconductor layer A2.

In step S400, using a fourth mask process, the intermediate insulatinglayer ILD and the gate insulating layer GI are patterned to form asource contact hole SH exposing one portion of the first semiconductorlayer A1 and a drain contact hole DH exposing another portion of thefirst semiconductor layer A1.

Here, steps S300, S310, and S400 may be changed in sequential order, inaccordance with the manufacturing conditions. For example, step S400 forforming the contact holes may be performed first, step S300 for formingthe second semiconductor layer A2 may be performed second, then stepS310 for performing the post-thermal treatment may be performed finally.Otherwise, step S300 for forming the second semiconductor layer A2 maybe performed first, step S400 for forming the contact holes may beperformed second, then step S310 for performing the post-thermaltreatment may be performed finally.

In step S500, a source-drain metal material is deposited on theintermediate insulating layer ILD. Using a fifth mask process, thesource-drain metal material is patterned to form a first sourceelectrode S1, a first drain electrode D1, a second source electrode S2and a second drain electrode D2.

In step S600, on the whole surface of the substrate SUB having thesource-drain electrodes, a passivation layer PAS is deposited.

First Application Example

The thin film transistor substrate having two different type thin filmtransistors on the same substrate, above explained, can be applied tovarious type display including the flat panel display, the flexibledisplay and/or the curved display. By forming the different two types ofthin film transistors on the same substrate, various advantages can beachieved. FIG. 5 is a block diagram illustrating a structure of thedisplay according to a first application example of the presentdisclosure. With reference to FIG. 5, advanced features and meritsexpected from the thin film transistor substrate according to a firstapplication example of the present disclosure will be explained.

The first and the second transistors T1 and T2 would be formed in eachpixel of the display panel 100 for switching the data voltage applied tothe pixel or for driving the pixel. In the case of an organic lightemitting diode display, the second thin film transistor T2 may be aswitch element for the pixel, and the first thin film transistor T1 maybe a driver element. In the interim, by combining the first and thesecond thin film transistors T1 and T2, they may be applied to oneswitch element or one driver element.

For a mobile device or a wearable device, in order to reduce the powerconsumption, the lower speed driving method using a low frame rate isadopted. In this case, the frame frequency may be lowered for stillimage and/or images having a slower update interval. Here, when usingthe lower frame rate, at every time for changing the data voltage, thebrightness of the display may be flashed. In some cases, as thedischarging time interval is elongated, the brightness may be flickeredat every data update period. By applying the first and the second thinfilm transistors T1 and T2 according to the present disclosure, theflicker problem at lower speed driving method can be prevented.

In the lower speed driving method, as the data update period iselongated, the leaked current amount of the switching thin filmtransistor may be increased. The leaked current of the switching thinfilm transistor may cause a voltage drop down of the storage capacitanceand a drop down of the voltage between gate and source. The second thinfilm transistor having the oxide semiconductor material can be appliedto the switch thin film transistor of the organic light emitting diodedisplay. Because the thin film transistor including the oxidesemiconductor material has lower off-current characteristics, thevoltage drop down of the storage capacitance and/or of the gateelectrode of the driving thin film transistor is prevented. The flickerphenomenon does not occur when using the lower speed driving method.

As poly crystalline silicon has the characteristics of high mobility, byapplying the first thin film transistor to the driving thin filmtransistor of the organic light emitting diode display, the currentamount supplied to the organic light emitting diode can be enlarged.Therefore, by applying the second thin film transistor T2 to theswitching thin film transistor and the first thin film transistor T1 tothe driving thin film transistor, the organic light emitting diodedisplay can achieve lower power consumption and better video quality.

As the thin film transistor substrate according to the presentdisclosure has excellent video quality without flickers even though thelower speed driving method is applied, it has a merit of being verysuitable for applying to the mobile display or the wearable display. Forthe example of wearable wrist watch, the video data may be updated atevery one second for reducing the power consumption. In that case, theframe frequency is 1 Hz. Using the arrangement of the presentdisclosure, excellent video quality without flickering can be achievedeven though the video data is driven with lower frequency, such as 1 Hzor less. Further, for the mobile display or the wearable display, theframe rate for the still image can be remarkably lowered, so that thepower consumption can be saved without any degradation of the videoquality. As the result, the video quality of the mobile display and/orwearable display, and the life time of the battery can be elongated. Inaddition, the present disclosure can be applied to the electric bookdevice (or ‘E-Book’) of which the data update period is very long,without any degradation of the video quality.

At least one of the first and the second thin film transistors T1 and T2may be embedded into a driver IC, for example shown in FIG. 5, e.g., anyone of the data driver IC 200, the multiplexer (or ‘MUX’) 210, and thegate driver IC 300, for forming the driver IC. This driver IC writesand/or applies the data voltage to the pixel. In another case, any oneof the first and the second thin film transistors T1 and T2 is disposedwithin the pixel, and the other is disposed in the driver IC. The datadriver IC 200 converts the input video data into the voltage values andoutput the voltage values. The multiplexer 210 may reduce the number ofthe output channel of the data driver 200, by distributing the datavoltages from the data driver 200 to the data lines DL by time-sharingor time-division method. The gate driver IC 300 outputs the scan signal(or ‘gate signal’) to the gate line GL synchronized to the data voltagefor sequentially selecting the pixel line where the data voltage isapplied. In order to reduce the output channel number of the gate driverIC 300, other multiplexers not shown in the figures may be furtherincluded between the gate driver IC 300 and the gate line GL. Themultiplexer 210 and the gate driver IC 300 may be formed on the samethin film transistor substrate within the pixel array, as shown in FIG.5. The multiplexer 210 and the gate driver IC 300 may be disposed withinthe non-display area NA and the pixel array may be disposed within thedisplay area AA, as shown in FIG. 5.

The thin film transistor substrate according to the present disclosuremay be applied to any type of active type display using an active matrixthin film transistor substrate, such as the liquid crystal display, theorganic light emitting diode display, and/or the electrophoresis displaydevice. Hereinafter, more application examples for the display using thethin film transistor substrate according to the present disclosure willbe explained.

Second Application Example

FIG. 6 is a plane view illustrating a thin film transistor substratehaving an oxide semiconductor layer included in a fringe field typeliquid crystal display according to a second application example of thepresent disclosure. FIG. 7 is a cross-sectional view illustrating thestructure of the thin film transistor substrate of FIG. 6 by cuttingalong the line I-I′ according to the second application example of thepresent disclosure.

The thin film transistor substrate having a metal oxide semiconductorlayer shown in FIGS. 6 and 7 comprises a gate line GL and a data line DLcrossing each other with a gate insulating layer GI therebetween on alower substrate SUB, and a thin film transistor T formed at eachcrossing portion. By the crossing structure of the gate line GL and thedata line DL, a pixel area is defined.

The thin film transistor T comprises a gate electrode G branched (or‘extruded’) from the gate line GL, a source electrode S branched fromthe data line DL, a drain electrode D facing the source electrode S, anda semiconductor layer A overlapping with the gate electrode G on thegate insulating layer GI for forming a channel area between the sourceelectrode S and the drain electrode D.

At one end of the gate line GL, a gate pad GP is disposed for receivingthe gate signal. The gate pad GP is connected to a gate pad intermediateterminal IGT through the first gate pad contact hole GH1 penetrating thegate insulating layer GI. The gate pad intermediate terminal IGT isconnected to the gate pad terminal GPT through the second gate padcontact hole GH2 penetrating the first passivation layer PA1 and thesecond passivation layer PA2. Further, at one end of the data line DL, adata pad DP is disposed for receiving the pixel signal. The data pad DPis connected to a data pad terminal DPT through the data pad contacthole DPH penetrating the first passivation layer PA1 and the secondpassivation layer PA2.

In the pixel area, a pixel electrode PXL and a common electrode COM areformed with the second passivation layer PA2 there-between, to form afringe electric field. The common electrode COM is connected to thecommon line CL disposed in parallel with the gate line GL. The commonelectrode COM is supplied with a reference voltage (or “common voltage”)via the common line CL. For other cases, the common electrode COM hasthe one sheet electrode shape which covers the whole surface of thesubstrate SUB except the drain contact hole DH portions. That is,covering over the data line DL, the common electrode COM can work as ashielding means for the data line DL.

The common electrode COM and the pixel electrode PXL can have variousshapes and positions according to the design purpose and environment.While the common electrode COM is supplied with a reference voltagehaving constant value, the pixel electrode PXL is supplied with a datavoltage varying timely according to the video data. Therefore, betweenthe data line DL and the pixel electrode PXL, a parasitic capacitancemay be formed. Due to the parasitic capacitance, the video quality ofthe display may be degraded. Therefore, it is preferable that the commonelectrode COM is disposed at the lower layer and the pixel electrode PXLis disposed at the topmost layer.

In other words, on the first passivation layer PA1 covering the dataline DL and the thin film transistor T, a planarization layer PAC isstacked thereon by thickly depositing an organic material having a lowpermittivity. Then, the common electrode COM is formed. And then, afterdepositing the second passivation layer PA2 to cover the commonelectrode COM, the pixel electrode PXL overlapping with the commonelectrode is formed on the second passivation layer PA2. In thisstructure, the pixel electrode PXL is far from the data line DL by thefirst passivation layer PA1, the planarization layer PAC and the secondpassivation layer PA2, so that it is possible to reduce the parasiticcapacitance between the data line DL and the pixel electrode PXL. Inother case, the pixel electrode PXL may be disposed at the lower layerand the common electrode COM is disposed at the topmost layer.

The common electrode COM may have a rectangular shape corresponding tothe pixel area. The pixel electrode PXL may have the shape of aplurality of segments. Especially, the pixel electrode PXL is verticallyoverlapped with the common electrode COM with the second passivationlayer PA2 there-between. Between the pixel electrode PXL and the commonelectrode COM, the fringe electric field is formed. By this fringeelectric field, the liquid crystal molecules arrayed in plane directionbetween the thin film transistor substrate and the color filtersubstrate may be rotated according to the dielectric anisotropy of theliquid crystal molecules. According to the rotation degree of the liquidcrystal molecules, the light transmittance ratio of the pixel area maybe changed so as to represent desired gray scale.

In FIGS. 6 and 7 for explaining the second application example of thepresent disclosure, in convenience, the thin film transistor T of theliquid crystal display is shown briefly. The first and/or the secondthin film transistors T1 and/or T2 explained from the first to secondembodiments of the present disclosure can be applied to this thin filmtransistor. In one example, for a low speed driving, the second thinfilm transistor T2 having the oxide semiconductor material can beapplied to the thin film transistor T. In another example, for low powerconsumption, the first thin film transistor T1 having the polycrystalline semiconductor material may be applied to the thin filmtransistor T. In still another example, the thin film transistor T maybe formed as including the first and the second thin film transistors T1and T2 and they are connected so that their performance andcharacteristics can compensate each other.

Third Application Example

FIG. 8 is a plane view illustrating the structure of one pixel for theactive matrix type organic light emitting diode display having theactive switching elements such as the thin film transistors according toa third application example of the present disclosure. FIG. 9 is a crosssectional view illustrating the structure of the organic light emittingdiode display along to the cutting line of II-IF in FIG. 8 according tothe third application example of the present disclosure.

With reference to FIGS. 8 and 9, the active matrix type organic lightemitting diode display comprises a switching thin film transistor ST, adriving thin film transistor DT connected to the switching thin filmtransistor ST, and an organic light emitting diode OLE connected to thedriving thin film transistor DT.

The switching thin film transistor ST is formed where a gate line GL anda data line DL are crossing each other, on a substrate SUB. Supplyingthe data voltage from the data line DL to the gate electrode DG of thedriving thin film transistor DT and to the storage capacitance STGreplying the scan signal, the switching thin film transistor ST acts forselecting the pixel which is connected to the switching thin filmtransistor ST. The switching thin film transistor ST includes a gateelectrode SG branching from the gate line GL, a semiconductor channellayer SA overlapping with the gate electrode SG, a source electrode SSand a drain electrode SD. Controlling the amount of the current appliedto the organic light emitting diode OLE of the pixel according to thegate voltage, the driving thin film transistor DT acts for driving theorganic light emitting diode OLE disposed at the pixel selected by theswitching thin film transistor ST.

The driving thin film transistor DT includes a gate electrode DGconnected to the drain electrode SD of the switching thin filmtransistor ST, a semiconductor channel layer DA, a source electrode DSconnected to the driving current line VDD, and a drain electrode DD. Thedrain electrode DD of the driving thin film transistor DT is connectedto the anode electrode ANO of the organic light emitting diode OLE.Between the anode electrode ANO and the cathode electrode CAT, anorganic light emitting layer OL is disposed. The cathode electrode CATis connected to the ground line Vss.

With more detailed reference to FIG. 9, on the substrate SUB of theactive matrix organic light emitting diode display, the gate electrodesSG and DG of the switching thin film transistor ST and the driving thinfilm transistor DT, respectively are disposed. On the gate electrodes SGand DG, the gate insulator GI is deposited. On the gate insulator GIoverlapping with the gate electrodes SG and DG, the semiconductor layersSA and DA are disposed, respectively. On the semiconductor layer SA andDA, the source electrodes SS and DS and the drain electrodes SD and DDfacing and separated from each other, respectively, are disposed. Thedrain electrode SD of the switching thin film transistor ST is connectedto the gate electrode DG of the driving thin film transistor DT via thedrain contact hole DH penetrating the gate insulator GI. The passivationlayer PAS is deposited on the substrate SUB having the switching thinfilm transistor ST and the driving thin film transistor DT.

A color filer CF is disposed at the area where the anode electrode ANOis disposed. It is preferable for the color filter CF to have a largearea as possible. For example, it is preferable to overlap with someportions of the data line DL, the driving current line VDD and/or thegate line GL. The upper surface of the substrate having these thin filmtransistors ST and DT and color filters CF is not in an even and/orsmooth condition, but in an uneven and/or rugged condition having manysteps. In order that the organic light emitting diode display has goodluminescent quality over the whole display area, the organic lightemitting layer OL should have an even or smooth surface. So, to make theupper surface in a planar and even condition, the planar layer PAC orthe overcoat layer OC is deposited on the whole surface of the substrateSUB.

Then, on the overcoat layer OC, the anode electrode ANO of the organiclight emitting diode OLED is disposed. Here, the anode electrode ANO isconnected to the drain electrode DD of the driving thin film transistorDT through the pixel contact hole PH penetrating the overcoat layer OCand the passivation layer PAS.

On the substrate SUB having the anode electrode ANO, a bank (or ‘bankpattern’) BA is disposed over the area having the switching thin filmtransistor ST, the driving thin film transistor DT and the various linesDL, GL and VDD, for defining the pixel area. The exposed portion of theanode electrode ANO by the bank BA is the light emitting area. On theanode electrode ANO exposed from the bank BA, the organic light emittinglayer OL is deposited. On the organic light emitting layer OL, thecathode electrode ACT is deposited. For the case that the organic lightemitting layer OL has a material emitting the white light, each pixelcan represent various colors by the color filter CF disposed under theanode electrode ANO. The organic light emitting diode display as shownin FIG. 9 is the bottom emission type display in which the visible lightis radiated to the bottom direction of the display substrate.

Between the gate electrode DG of the driving thin film transistor DT andthe anode electrode ANO, a storage capacitance STG may be formed. Byconnected to the driving thin film transistor DT, the storagecapacitance STG keeps the voltage supplied to the gate electrode DG ofthe driving thin film transistor DT from the switching thin filmtransistor ST in stable condition.

Using the thin film transistor substrate like the above explanations, anactive type flat panel display having good properties can be acquired.Especially, to ensure excellent driving properties, it is preferablethat the active layer of the thin film transistor would include a metaloxide semiconductor material.

The metal oxide semiconductor material may be degraded when it isworking exposed by the light for a long time. Therefore, it ispreferable that the thin film transistor having a metal oxidesemiconductor material has a structure for blocking light from outsideof the upper portion and/or the lower portion of the thin filmtransistor. For example, for the above mentioned thin film transistorsubstrates, it is preferable that the thin film transistor would beformed in the bottom gate structure. That is, the light induced from theoutside of the substrate, especially from the lower side of thesubstrate facing the observer, can be blocked by the gate electrode Gincluding an opaque metal material.

The thin film transistor substrate for the flat panel display has aplurality of pixel area disposed in a matrix manner. Further, each pixelarea includes at least one thin film transistor. That is, over the wholesubstrate, a plurality of thin film transistor is disposed. Theplurality of pixel area and the plurality of thin film transistor areused for the same purpose and they should have the same quality andcharacteristics, so that they have the same structure.

However, in some cases, the thin film transistors may be formed ashaving different characteristics from each other. For the example of theorganic light emitting diode display, in one pixel area, at least oneswitching thin film transistor ST and at least one driving thin filmtransistor DT are disposed. As the purposes of the switching thin filmtransistor ST and the driving thin film transistor DT are different fromeach other, the characteristics of the two are different from each otheras well. To do so, the switch thin film transistor ST and the drivingthin film transistor DT may have the same structure and the samesemiconductor material, but the channel layers of them have differentsizes for optimizing their characteristics. Otherwise, a compensatingthin film transistor may further be included for supporting any specificfunctions or properties of any thin film transistor.

In FIGS. 8 and 9, the switching thin film transistor ST and the drivingthin film transistor DT of the organic light emitting diode display ofthe third application example are shown. The first and/or the secondthin film transistors T1 and/or T2 explained from the first to secondembodiments of the present disclosure can be applied to this thin filmtransistor. For example, the second thin film transistor T2 having theoxide semiconductor material can be applied for the switching thin filmtransistor ST. The first thin film transistor T1 having the polycrystalline semiconductor material may be applied for the driving thinfilm transistor DT. Therefore, by including the first and the secondthin film transistors T1 and T2 on one substrate, their performance andcharacteristics can compensate each other.

Fourth Application Example

For still another example, a driver element (or ‘driver IC’) may beformed in the non-display area of the same thin film transistorsubstrate for the flat panel display. Hereinafter, with reference toFIGS. 10 and 11, a thin film transistor substrate having the driver ICon the same substrate will be explained.

FIG. 10 is an enlarged plane view illustrating a structure of an organiclight emitting diode display according to a fourth application exampleof the present disclosure. FIG. 11 is a cross sectional viewillustrating a structure of the organic light emitting diode displayalong to the cutting line of III-III′ in FIG. 10 according to a fourthapplication example of the present disclosure. Here, as the explanationfor the thin film transistor substrate having a driver therein issimilar, a detailed explanation about the thin film transistor substrateand the organic light emitting diode will be omitted.

The plane structure of the organic light emitting diode displayaccording to the fourth application example will be explained in detailwith reference to FIG. 10. An organic light emitting diode displayaccording to the fourth application example comprises a substrate SUBincluding a display area AA for representing the video information and anon-display area NA having various elements for driving the elements inthe display area AA. In the display area AA, a plurality of pixel areasPA disposed in a matrix manner are defined. In FIG. 10, the pixel areaPA is illustrated as the dotted line.

For example, the pixel areas PA can be defined as an N (row)×M (column)matrix. However, the disposed pattern is not restricted this manner, buthas various types. Each of the pixel area PA has the same size or adifferent size. With one unit pixel having three sub pixels includingred (R), green (G) and blue (B) sub pixels, the unit pixels areregularly disposed. Explaining with a simple structure, the pixel areaPA can be defined by the crossing structure of a plurality of gate linesGL running in a horizontal direction and a plurality of data lines DLrunning in a vertical direction.

In the non-display area NA defined as the peripheral area surroundingthe pixel area PA, a data driving integrated circuit DIC for supplyingthe video data to the data line DL and a gate driving integrated circuitGIP for supplying the scan signal to the gate line GL are disposed. Fora case of a higher resolution display panel than a VGA panel in whichmore data lines DL and more driving current lines VDD may be used, thedata driving integrated circuit DIC may be externally installed from thesubstrate SUB, and data contact pads may be disposed on the substrateSUB instead of the data driving integrated circuit DIC.

In order to simply show the structure of the display, the gate drivingintegrated circuit GIP is formed on one side portion of the substrateSUB directly. The ground line Vss for supplying the ground voltage maybe disposed at the outermost side of the substrate SUB. The ground lineVss is disposed so as to receive the ground voltage from an externaldevice located out of the substrate SUB, and to supply the groundvoltage to the data driving integrated circuit DIC and the gate drivingintegrated circuit GIP. For example, the ground line Vss may be linkedto the data driving integrated circuit DIC disposed at the upper side ofthe substrate SUB and to the gate driving integrated circuit GIPdisposed at the right side and/or left side of the substrate SUB so asto surround the substrate SUB.

At each pixel area PA, the main elements such as an organic lightemitting diode and thin film transistors for driving the organic lightemitting diode are disposed. The thin film transistor is disposed at thethin film transistor area TA defined at one side of the pixel area PA.The organic light emitting diode includes an anode electrode ANO, acathode electrode CAT and an organic light emission layer OL insertedbetween these two electrodes. The actual emission area is decided by thearea of the organic light emission layer OL overlapping the anodeelectrode ANO.

The anode electrode ANO has a shape as to occupy some area of the pixelarea PA and is connected to the thin film transistor formed in the thinfilm transistor area TA. The organic light emission layer OL isdeposited on the anode electrode ANO. The cathode electrode CAT isdeposited on the organic light emission layer OL so as to cover a wholesurface of the display area AA having the pixel areas PA.

The cathode electrode CAT may go over the gate driving integratedcircuit GIP and contact the ground line Vss disposed at the outer side.So, the ground voltage can be supplied to the cathode electrode CATthrough the ground line Vss. The cathode electrode CAT receives theground voltage and the anode electrode ANO receives the voltagecorresponding to the video data and then, by the voltage differencebetween the cathode electrode CAT and the anode electrode ANO, theorganic light emission layer OL radiates the light to represent thevideo information.

The cross-sectional structure of the organic light emitting diodedisplay according to the fourth application example will be explained indetail with reference to FIG. 11. On the substrate SUB, a non-displayarea NA and a display area AA are defined. The non-display area NAincludes an area where the gate driving integrated circuit GIP and theground line Vss are disposed. The display area AA includes an area wherea switching thin film transistor ST, a driving thin film transistor DTand an organic light emitting diode OLE are defined.

The gate driving integrated circuit GIP has thin film transistors whichare formed when the switching thin film transistor ST and the drivingthin film transistor DT are formed. The switching thin film transistorST in the pixel area PA has a gate electrode SG, a gate insulating layerGI, a channel layer SA, a source electrode SS and a drain electrode SD.In addition, the driving thin film transistor DT has a gate electrode DGconnected to the drain electrode SD of the switching thin filmtransistor ST, the gate insulating layer GI, a channel layer DA, asource electrode DS and a drain electrode DD.

On the thin film transistors ST and DT, a passivation layer PAS and aplanar layer PL are sequentially deposited. On the planar layer PL, ananode electrode ANO having an isolation shape within the pixel area PAis disposed. The anode electrode ANO connects to the drain electrode DDof the driving thin film transistor DT through the contact holepenetrating the passivation layer PAS and the planar layer PL.

On the substrate SUB having the anode electrode ANO, a bank BA isdeposited for defining the emission area. By patterning the bank BA, themost center portions of the anode electrode ANO are exposed. On theexposed anode electrode ANO, an organic light emission layer OL isdeposited. Depositing a transparent conductive material on the bank BAand the organic light emission layer OL, the cathode electrode CAT isstacked. The organic light emitting diode OLED including the anodeelectrode ANO, the organic light emission layer OL and the cathodeelectrode CAT is disposed.

In the case that the organic light emission layer OL may generate thewhite lights, color filters CF may be further included for representingfull color video information. In that case, the organic light emissionlayer OL would be preferably deposited as covering the whole surface ofthe display area AA.

The cathode electrode CAT is expanded over the gate driving integratedcircuit GIP so that it may cover the display area AA and the non-displayarea NA and contact the ground line Vss disposed at the outercircumstance of the substrate SUB. As a result, the ground (or,reference) voltage can be supplied to the cathode electrode CAT via theground line Vss.

In addition, the ground line Vss may be formed at the same layer andmade of the same material with the gate electrodes SG and DG. In thatcase, the cathode electrode CAT can be connected to the ground line Vssthrough the contact hole penetrating the passivation layer PAS and thegate insulating layer GI over the ground line Vss. Otherwise, the groundline Vss may be formed at the same layer and made of the same materialwith the source-drain electrodes SS-SD and DS-DD. In this case, thecathode electrode CAT can be connected to the ground line Vss throughthe contact hole penetrating the passivation layer PAS over the groundline Vss.

In FIGS. 10 and 11, the switching thin film transistor ST and thedriving thin film transistor DT of the organic light emitting diodedisplay of the fourth application example are shown. The first and/orthe second thin film transistors T1 and/or T2, explained in the first tosecond embodiments of the present disclosure, can be applied to thesethin film transistors. For example, the second thin film transistor T2having the oxide semiconductor material can be applied for the switchingthin film transistor ST. The first thin film transistor T1 having thepoly crystalline semiconductor material may be applied for the drivingthin film transistor DT. Further, for the gate driver IC GIP, the firstthin film transistor T1 having the poly crystalline semiconductormaterial may be applied. For example, for the gate driver IC GIP, theC-MOS type thin film transistor may include P-MOS type and N-MOS typethin film transistors.

A thin film transistor substrate for a flat panel display and a displayusing the same according to the present disclosure comprises twodifferent types of thin film transistors on the same substrate so thatthe disadvantage of any one type of thin film transistor can becompensated by the other type of thin film transistor. For example, witha thin film transistor having low frequency driving characteristics, thedisplay can have the low power consumption property, and the display canbe applied to the portable and/or wearable appliances.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the thin film transistorsubstrate and display using the same of the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A display, comprising: a first thin filmtransistor including a poly crystalline semiconductor layer, a firstgate electrode on the poly crystalline semiconductor layer, a firstsource electrode, and a first drain electrode; a second thin filmtransistor including a second gate electrode, an oxide semiconductorlayer on the second gate electrode, a second source electrode, and asecond drain electrode; and an intermediate insulating layer including anitride layer and an oxide layer on the nitride layer, the intermediateinsulating layer disposed on the first gate electrode and the secondgate electrode and under the oxide semiconductor layer.
 2. The deviceaccording to claim 1, further comprising a driver, wherein at least oneof the first thin film transistor and the second thin film transistor isdisposed in a pixel, and wherein at least one of the first thin filmtransistor and the second thin film transistor is disposed at thedriver.
 3. The device according to claim 1, further comprising a gateinsulating layer covering the poly crystalline semiconductor layer. 4.The device according to claim 3, wherein the first gate electrode andthe second gate electrode are formed on the gate insulating layer. 5.The device according to claim 1, wherein the second thin film transistoris a switching element for selecting a pixel, and wherein the first thinfilm transistor is a driving element for driving an organic lightemitting diode of the pixel selected by the second thin film transistor.6. The device according to claim 2, wherein the driver includes: a datadriver configured to output a data voltage; a multiplexer configured todistribute the data voltage from the data driver to a data line; and agate driver configured to output a scan pulse to a gate line, wherein atleast one of the first thin film transistor and the second thin filmtransistor is disposed at any one of the multiplexer and the gatedriver.
 7. The device according to claim 3, wherein a portion of thefirst source electrode is disposed on the intermediate insulating layer,and connected to a first portion of the poly crystalline semiconductorlayer through a source contact hole penetrating the intermediateinsulating layer and the gate insulating layer, wherein a portion of thefirst drain electrode is disposed on the intermediate insulating layer,and connected to a second portion of the poly crystalline semiconductorlayer through a drain contact hole penetrating the intermediateinsulating layer and the gate insulating layer, wherein the secondsource electrode contacts a first portion of the oxide semiconductorlayer on the intermediate insulating layer, and wherein the second drainelectrode contacts a second portion of the oxide semiconductor layer onthe intermediate insulating layer.
 8. The display device according toclaim 1, wherein each of the nitride layer and the oxide layer has athickness of 1,000 Å˜3,000 Å.
 9. The display device according to claim1, wherein the intermediate insulating layer includes a lower oxidelayer under the nitride layer and on the first and the second gateelectrodes.
 10. A display, comprising: a first semiconductor layerincluding a poly crystalline semiconductor material; a gate insulatinglayer covering the first semiconductor layer; a first gate electrodedisposed on the gate insulating layer and overlapping the firstsemiconductor layer; a second gate electrode disposed on the gateinsulating layer; an intermediate insulating layer including a nitridelayer and an oxide layer on the nitride layer, and covering the firstgate electrode and the second gate electrode; a second semiconductorlayer disposed on the intermediate insulating layer, including an oxidesemiconductor material and overlapping the second gate electrode; afirst source electrode and a first drain electrode disposed on theintermediate insulating layer; and a second source electrode, and asecond drain electrode disposed on the second semiconductor layer. 11.The device according to claim 10, wherein the first semiconductor layer,the first gate electrode, the first source electrode and the first drainelectrode are included in a first thin film transistor, and wherein thesecond semiconductor layer, the second gate electrode, the second sourceelectrode, and the second drain electrode are included in a second thinfilm transistor.
 12. The device according to claim 11, furthercomprising a driver, wherein at least one of the first thin filmtransistor and the second thin film transistor is disposed in a pixel,and wherein at least one of the first thin film transistor and thesecond thin film transistor is disposed at the driver.
 13. The deviceaccording to claim 11, wherein the second thin film transistor is aswitching element for selecting a pixel, and wherein the first thin filmtransistor is a driving element for driving an organic light emittingdiode of the pixel selected by the second thin film transistor.
 14. Thedisplay device according to claim 12, wherein the driver includes: adata driver outputting a data voltage; a multiplexer distributing thedata voltage from the data driver to a data line; and a gate driveroutputting a scan pulse to a gate line, wherein at least one of thefirst thin film transistor and the second thin film transistor isdisposed at any one of the multiplexer and the gate driver.
 15. Thedevice according to claim 10, wherein the first source electrode isconnected to a first portion of the first semiconductor layer through asource contact hole penetrating the intermediate insulating layer andthe gate insulating layer, wherein the first drain electrode isconnected to a second portion of the first semiconductor layer through adrain contact hole penetrating the intermediate insulating layer and thegate insulating layer, wherein the second source electrode contacts afirst portion of the second semiconductor layer, and wherein the seconddrain electrode contacts a second portion of the second semiconductorlayer.
 16. The device according to claim 10, wherein the nitride layerand the oxide layer have a thickness of 1,000 Å˜3,000 Å.
 17. The deviceaccording to claim 10, wherein the intermediate insulating layerincludes a lower oxide layer under the nitride layer and on the firstand the second gate electrodes.